This invention relates to a vessel propulsion system, and more particularly, to a propulsion system for vessels of a type utilizing the reaction force of discharged water jets for forward or backward travel.
A water jet propulsion system without protrusions such as a propeller and helm at the vessel bottom can be free from entanglement of string-like drifting matters, allowing the vessel to travel on shallow water.
A conventional water jet propulsion system draws water by suction from a suction casing opening at the hull bottom, guiding drawn water to a pump casing, pressurizing with an impeller, and discharges pressurized water rearward as flux of water jets from a delivery casing opening at the stern at a level above the draft, making use of the reaction force to propel the vessel forward.
In particular, a water jet propulsion system disclosed in Japanese Patent Application Laying-Open Publication No. Hei 11-124090 is adapted by a deflector for changing the discharge direction of water jets to turn the course of travel, and by a reverser for reversing water jets to propel the vessel rearward.
The conventional water jet propulsion system, which allows the vessel to travel backward by reversing water jets discharged behind the stern toward the bow, has a great power loss, and gives a wide range of turn to the vessel coming alongside or leaving a pier, with the propelling force to be weak upon reversal of water jets.
Japanese Patent Application Laying-Open Publication No. Hei-5-105190 discloses a counter-rotating double-impeller type water jet propulsion system including a combination of a front impeller for generating swirling streams and a rear impeller for rectifying them into straight streams to convert energy of rotation into thrust forces, to have an increased propelling force.
This invention aims at provision of a vessel propulsion system which employs the reaction of water jet discharge to provide a vessel propelling force, and which has a minimized energy loss upon switch between forward and rearward movements, allowing for the vessel to come alongside or leave a pier within a narrowed range.
An aspect of the invention is a vessel propulsion system, which comprises a vessel propulsion system comprising a suction casing configured with a suction inlet opening at a vessel bottom, a suction flow path inclined to rearwardly ascend from the suction inlet, and an impeller chamber formed horizontal, and disposed at a bottom part of a stern, a delivery casing connected to the suction casing and submerged under a draft of the stern, and a set of forward and reverse rotatable axial flow blades disposed in the impeller chamber of the suction casing.
According to this aspect of the invention, the impeller in a pump casing is adapted for reverse rotation to draw water by suction from a delivery outlet of the delivery casing, which discharges jets of pressurized water in a forward travel, and to discharge jets of pressurized water from the suction inlet of the suction casing, thus switching the suction inlet of water and the delivery outlet of pressurized water jets therebetween, enabling switch from forward travel to backward travel.
The impeller chamber of the suction casing and the delivery casing may preferably be formed circular cylindrical at inside diameters thereof to be substantially identical in size. This arrangement substantially equalizes respective amounts of water to be pressurized and swirled by forward rotation and reverse rotation of axial flow blades, allowing for a rapid switching between forward travel and backward travel of vessel.
A single stage of axial flow blades may preferably be disposed in the impeller chamber of the suction casing, and axial flow blades may preferably be configured as a counter-rotating double-impeller. In this arrangement, swirling streams of water pressurized by an axial flow type front impeller may be converted into straight streams by a rear impeller, to thereby convert energy of swirling streams into pressure exerting energy, with an increased impeller efficiency relative to the single stage impeller.
A forward-reverse rotation effecter may preferably be coupled for connection at a side wall of the suction casing in which the impeller chamber has a counter-rotating double-impeller disposed therein. This arrangement allows a drive shaft of the counter-rotating double-impeller to be short, and the front impeller and the rear impeller to have reduced vibrations. A forward-reverse rotation shifter may preferably be coupled for connection at a side wall of the suction casing in which the impeller chamber has a single stage of axial flow blades disposed therein, which allows the propulsion system to be compact.
The delivery casing may preferably have a bearing support fixed on an inner peripheral wall thereof for rotatably supporting a distal end of a drive shaft, the bearing support having thereon a plurality of ribs formed planer along an axis thereof so that swirling water streams pressurized by the set of axial flow blades are rectified by the bearing support, whereby the distal end of the drive shaft can be rotatably supported near axial flow blades, with reduced vibrations.
A deflector may preferably be disposed at a rear end of the delivery casing, having a helm fixed thereto, which allows the course holding performance to be improved in a turning travel, as well as the steering performance, with effective roll prevention, in addition to possible turning backward travel by the deflector to be turned left or right.
A pair of vessel propulsion systems may preferably be arranged at the vessel stern, allowing for the vessel to turn within a narrowed range, with possible transverse displacement and facilitated approach to and departure from a pier.
There may preferably be provided a vessel-side fronting branch path branched from the delivery casing having a rearward casing cooperative therewith for flow path selection therebetween, which allows a transverse propulsion.